Ask if it is first, and then why. Which parrot is female? Which is male? 
Eclectic parrots ordinary people may directly judge that the red one is male.
But in reality, the green ones are the males. Some people might say that even though males are not necessarily prettier, they should always be stronger, right? The humble lifelong male monkfish has something to say. 
In the picture, a female monkfish.
Where are the male monkfish? In this:
How humble is the life of a male monkfish?
It was born to find a female monkfish. Unable to find a female, it will not be able to grow and mature, and will even die because it is difficult to eat. After finding a female, the moment she bites her body, the female secretes special digestive enzymes to stick to it. The mouth melts and is directly connected to the circulatory system of the female body, becoming a parasitic relationship. Looks good, and eats worry-free for a lifetime. However, the cruel truth is that the eyes and internal organs of the male monkfish will deteriorate, and eventually only fertility will be retained. Extreme cases like monkfish, which are not common in the animal kingdom. But it can also be seen that the relationship between male and female has various possibilities. In fact, there are a large number of animals in the animal kingdom that do not have obvious differences in appearance between males and females. For example: octopuses, butterflies, penguins, rabbits, etc. So why do some species exhibit a stark contrast between male and female? For example, the gorgeous bird of paradise. 
Essentially, the differences in gender characteristics mainly come from the choice of the sexes. In order to achieve reproductive success, biological individuals always tend to look for the best mates. Different animals have different strategies for selecting the sexes, which can lead to a wide variety of their traits. And sexual selection does not always depend on vision. For example, in frogs and cicadas, males mainly attract females through their sounds. The male frog has evolved a loud sound, while the male cicada's abdomen has evolved a specialized vocalizer. 
On the right is a male cicadaThere are also some animals, and the cost of sexual selection, has been raised to unprecedented levels. For example, female bees mate with multiple male peaks at a time of mating and store sperm throughout their lives. Typical bee colonies have many males, but only a few males have the right to mate. [1]
This determines that the female bees have absolute sexual selection, and they only need to increase their body size to ensure strong reproductive ability.
As the selected object, Xiongfeng must increase the input of its own reproductive costs. Even the sexual selection of some animals can even threaten the survival of the individual. [2] For example, the viability of male osum bugs will be greatly reduced during the opossum period (the picture will not be released, and those who are interested can learn about it on their own, and the intensive fear warning). In the process of gender selection, the active and passive sexual selection plays a decisive role in the evolution of traits. The party with the initiative to choose will evolve a particular preference for a certain trait and behavior. Because of the existence of reproductive competition pressure, in the process of evolution, these traits or behaviors will be continuously iteratively strengthened, and then develop in a more complex and refined direction. Whether it's the feathers and dance of the male Magnificent Elysium, or the tail of the peacock, or the courtship pavilion of the male gardener's bird, they all evolved because of the female's selection preferences:
For birds in which females dominate sexual selection, we assume that initially males and females have the same color of feathers, as well as nesting ability.
Females with dominant sexual selection will use their plumage color to select healthier males, and nesting ability to select males with stronger reproductive contributions. Male birds naturally evolve iteratively in this direction. On the contrary, female birds do not have such competitive pressure. After a few generations, the differences in the plumage of the males and females will increase, and as the males become more capable of nesting, some females will stop nesting altogether. Females develop sexual selection preferences, which again reinforces sexual selection for males. While traits such as the male peacock's tail have greatly affected their ability to survive, the female peacock's selective preference is already engraved in the genes, and they will choose more "beautiful" males because of their selective preference. 
This goes far beyond choosing a mate for the sake of health and reproduction.
The word "involution" can almost be perfectly used here for this "useless" sexual selection. Mammals tend to be more "violent" in sexual selection than in birds. Not only do males need to compete with each other, but males even need to resist against females. [3] Even high levels of testosterone in males can directly promote muscle growth for sexual competition. In this relationship, male mammals, although active in sexual selection, evolve in the direction of highly male hormonal characteristics, such as well-developed muscles and strong physique. This is especially true in large mammals. Both herbivorous elephants and carnivorous lions show brutal sexual competition among males. Of course, due to the sexual selection preference of females, other traits may also be present, such as the mane of male lions. 
In general, unlike birds, who give the initiative of sexual selection to females through "literary competition", male mammals mainly decide the right to choose through martial arts, and then conquer females. As a result, male mammals have a higher level of sexual initiative than birds.
As mammals, human beings naturally have mammalian commonalities in sexual selection. However, in addition to the sexual selection of male male hormonal characteristics, the sexual selection of human beings has its own distinctive characteristics. Humans evolved from Australopithecus, and due to the improvement of intelligence and the change of social structure, human sexual selection has become far more complex than that of ordinary animals. Compared to other higher primates, humans not only have higher brain volumes, but also have longer childhoods and juvenile traits (adult humans share some of the physical characteristics of juvenile chimpanzees). Some evolutionary biologists believe that such characteristics in humans are caused by sexual selection. [4] There are even studies that show that the improvement of human intelligence is also related to the selection of the sexes. For example, men with too small heads show less competitiveness in gender selection. [5] Although the ** characteristic of humans is due to the loss of body hair during evolution, which favors sweating. [6] However, Darwin believed that sexual selection was involved, and some modern biologists continued Darwin's view. But at the very least, sexual selection provides an evolutionary impetus for the advancement of human beings.
Distant human ancestors and chimpanzees had similar hair volumesAmong sexual selection, the most typical is that humans do not have estrus. The reason why there is no estrus period is mainly because the woman "hides" the ovulation period.
There are various hypotheses to explain the hidden ovulation period of women, such as: paternity investment hypothesis, reduced infanticide hypothesis, social connection hypothesis, sexual reward hypothesis, and adultery hypothesis.
Although in the process of evolution, the content mentioned in these hypotheses is sufficient for the "hidden" ovulation period of women. But in terms of physiological characteristics, it should be closer to the truth.
Female mammals, including apes, tend to attract males during estrus by swelling**, but after walking upright, the field of vision is detached**. Women's ** signals are not only becoming more and more useless, but they also affect walking. In early human society, selection pressure was formed in the harsh environment, so that women in hidden estrus were selected. [7] Due to the increase in human brain volume, women are extremely prone to dystocia, which allows women with larger pelvis to win the reproductive competition. Humans have a longer infancy period, and women with larger breasts are more likely to breastfeed (round breasts, which are also a signal for fertility [8]). In women, the impact of age on fertility is much higher than that of men, which will make men have a younger sexual selection preference when choosing a mate, resulting in a bias towards juvenile characteristics in the process of female evolution (Eastern adult women have higher juvenile characteristics than Western adult women, and it is very likely to be the long-term choice of male sexual preference in classical civilization). In short, in the process of evolution, the reproductive characteristics of women will form a preference for male sexual selection. This preference for selection reinforces the evolution of a woman's pelvic cavity and breast size.
Feminine features in stick figures, however, lie in the complexity of human society, which is that there is a stronger choice between the sexes, not just men choosing women. Purely in terms of body shape (excluding the material influence of human society), women are significantly more inclined to choose men with higher testosterone levels.
There is an opinion that the reason why male humans do not have ** bones is the reason for female sexual selection. The ability to have a pure congested erection without ** bone can often reflect the physical and mental health of men to a certain extent. [9] The size of apes** is determined by sperm competition, but human males are larger, and there is an element of female sexual selection. [10] It is also believed that the size of the tin is related to the chance of conception, and can directly determine the sexual competitiveness of men. [11] The choice between the sexes is also manifested in the attraction of the sexes to each other. The body odor characteristics of men that attract women are ** the human pheromone androstenedione.
The feeling that androstenedione brings to women is not necessarily body odor, but may be the feeling of smelling comfortable and good.
Similarly, the release of estrotetraenes in women's bodies may be the root cause of some people's belief that women have natural body odor. Overall, in terms of biology alone, sexual selection is highly complex, far more complex than other mammals.
However, human society also has a complex social structure. Differences in money, fame, and status can greatly affect the choice of both sexes. Substance selection can reduce the pressure of sexual selection in men's appearance. However, in a patriarchal society, the existence of male sexual choice preference will lead to increased pressure on women's sexual selection. The complex choice of the sexes has caused the differences in the body posture of men and women today. But aesthetics have ethnic preferences. For example, people who worship strength more may feel that strong men are more beautiful, and even women will have a need to be physically strong. The Han Dynasty Wei and Jin Dynasty were masculine, and the Tang Dynasty was beautiful with plumpness. Even if individual differences are excluded, under different social and cultural environments, it is not absolute who is more beautiful than men and women. It is not difficult to predict that with the development of science and technology, the physical survival pressure of human beings is getting lower and lower, and the choice of the sexes in the future will depend more on the sexual aesthetic preferences of men and women (after the actual society is sufficiently developed, the role of material conditions in the choice of the sexes will gradually decrease). However, no matter how the aesthetic preferences change, as long as the sex hormones of men and women do not change, androstenedione and estradioene still play their role, and the unique sexual body characteristics of men and women are always the mainstream of sexual attraction between the sexes. References:
1] guide, t. r. social insects : bees, wasps, ants and termites teacher resource guide. (2011)
2] darwin, charles; a. r. wallace (1858). "on the tendency of species to form varieties; and on the perpetuation of varieties and species by natural means of selection" (pdf). journal of the proceedings of the linnean society of london. zoology. 3 (9): 46–50. doi:10.1111/j.1096-3642.1858.tb02500.x. archived (pdf) from the original on 2012-10-22.
3] evolution and human beh**ior: darwinian perspectives on human nature
4] shea, brian t. (1989). "heterochrony in human evolution: the case for neoteny reconsidered". american journal of physical anthropology. 32 (s10): 69–101. doi:10.1002/ajpa.1330320505.
6] jablonski, n. g. (2006). skin: a natural history. berkeley, ca: university of california press. p. pp13.
7] pawłowski, b. loss of oestrous and concealed ovulation in human evolution. (1999) current anthropology 40 (3): 257-276
8] morris, desmond (2007). "breasts". the naked woman. isbn 978-0-312-33853-4.
9] dawkins, richard (2006) [first published 1976]. the selfish gene (30th anniversary ed.).p. 158 endnote. it is not implausible that, with natural selection refining their diagnostic skills, females could glean all sorts of clues about a male's health, and the robustness of his ability to cope with stress, from the tone and bearing of his penis.
10] miller, g.f. (1998), "how mate choice shaped human nature: a review of sexual selection and human evolution" in handbook of evolutionary psychology.
11] in a theoretical **published in the journal evolutionary psychology in 2004, gallup and coauthor, rebecca burch, conjecture that, "a longer penis would not only h**e been an advantage for le**ing semen in a less-accessible part of the vagina, but by filling and expanding the vagina, it also would aid and abet the displacement of semen left by other males as a means of maximizing the likelihood of paternity." – "secrets of the phallus: why is the penis shaped like that?", scientificamerican.com.